Add an example of a connection pool

Change-Id: I70ff7a43ac77f07c7dfe10d5fe45eac230cffc60
Reviewed-on: http://review.couchbase.org/28947
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Reviewed-by: Matt Ingenthron <matt@couchbase.com>